Inter symbol interference (ISI) resulting from a communications channel can greatly reduce an eye opening at an input of a receiver. A decision feedback equalizer (DFE) can be used to reduce ISI. However, reflections in the communications channel can cause ISI in a wide range of symbols. To reduce ISI in the wide range of symbols, the DFE needs a large number of taps.
At higher data rates (i.e., above 17 Gbps), implementation of a digital decision feedback equalizer (DFE) becomes increasingly difficult. One reason for the difficulty is that ensuring the first tap feedback is stable within one symbol interval becomes increasingly challenging, because the symbol interval gets smaller as the data rate increases. Unrolling the DFE helps to relax the timing constraint. However, unrolling is done at the cost of the number of capture latches, which increases exponentially with the number of DFE taps. A linear equalizer (LE), such as a feed forward equalizer (FFE) or a continuous time linear equalizer, could be used as an alternative, but such linear equalizers can only handle channels without reflections.
It would be desirable to have an equalizer that can be used on higher data rate channels with reflections.